[PATCH v10 53/59] resources: Make allocate_resource() return best fit resource

[Yinghai Lu]

Current code just allocate from first avail window.

We can find all suitable empty slots and pick one with smallest size, so
we could save the big slot for needed ones later when we have several pci
bridges under parent bridge and some bridges get assigned from bios and we
need to assign others in kernel.

For examples: we have window
[0xc0000000, 0xd0000000), and [0xe0000000,0xe1000000)

and we try allocate 0x200000 size resource.

in this patch will reserve [0xc0000000, 0xd0000000) and
[0xe0000000,0xe1000000) at first, then pick [0xe0000000,0xe1000000)
to allocate 0x200000 size.

Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
---
 kernel/resource.c | 76 ++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 61 insertions(+), 15 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 3d7cf0b..c2724cd 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -589,7 +589,7 @@ static void resource_clip(struct resource *res, resource_size_t min,
  * alignment constraints
  */
 static int __find_resource(struct resource *root, struct resource *old,
-			 struct resource *new,
+			 struct resource *new, struct resource *availx,
 			 resource_size_t  size,
 			 struct resource_constraint *constraint)
 {
@@ -629,6 +629,11 @@ static int __find_resource(struct resource *root, struct resource *old,
 			if (resource_contains(&avail, &alloc)) {
 				new->start = alloc.start;
 				new->end = alloc.end;
+				if (availx) {
+					availx->start = avail.start;
+					availx->end = avail.end;
+					availx->flags = avail.flags;
+				}
 				return 0;
 			}
 		}
@@ -643,16 +648,6 @@ next:		if (!this || this->end == root->end)
 	return -EBUSY;
 }
 
-/*
- * Find empty slot in the resource tree given range and alignment.
- */
-static int find_resource(struct resource *root, struct resource *new,
-			resource_size_t size,
-			struct resource_constraint  *constraint)
-{
-	return  __find_resource(root, NULL, new, size, constraint);
-}
-
 /**
  * reallocate_resource - allocate a slot in the resource tree given range & alignment.
  *	The resource will be relocated if the new size cannot be reallocated in the
@@ -672,8 +667,8 @@ static int reallocate_resource(struct resource *root, struct resource *old,
 	struct resource *conflict;
 
 	write_lock(&resource_lock);
-
-	if ((err = __find_resource(root, old, &new, newsize, constraint)))
+	err = __find_resource(root, old, &new, NULL, newsize, constraint);
+	if (err)
 		goto out;
 
 	if (resource_contains(&new, old)) {
@@ -701,10 +696,16 @@ out:
 	return err;
 }
 
+struct good_resource {
+	struct list_head list;
+	struct resource avail;
+	struct resource new;
+};
 
 /**
  * allocate_resource - allocate empty slot in the resource tree given range & alignment.
- * 	The resource will be reallocated with a new size if it was already allocated
+ *	The resource will be reallocated with a new size if it was already
+ *	allocated
  * @root: root resource descriptor
  * @new: resource descriptor desired by caller
  * @size: requested resource region size
@@ -725,6 +726,9 @@ int allocate_resource(struct resource *root, struct resource *new,
 {
 	int err;
 	struct resource_constraint constraint;
+	LIST_HEAD(head);
+	struct good_resource *good, *tmp;
+	resource_size_t avail_size = (resource_size_t)-1ULL;
 
 	if (!alignf)
 		alignf = simple_align_resource;
@@ -741,11 +745,53 @@ int allocate_resource(struct resource *root, struct resource *new,
 		return reallocate_resource(root, new, size, &constraint);
 	}
 
+	/* find all suitable ones and add to the list */
+	for (;;) {
+		good = kzalloc(sizeof(*good), GFP_KERNEL);
+		if (!good) {
+			err = -ENOMEM;
+			break;
+		}
+
+		good->new.start = new->start;
+		good->new.end = new->end;
+		good->new.flags = new->flags;
+
+		write_lock(&resource_lock);
+		err = __find_resource(root, NULL, &good->new, &good->avail,
+					size, &constraint);
+		if (err || __request_resource(root, &good->avail)) {
+			err = -EBUSY;
+			kfree(good);
+			write_unlock(&resource_lock);
+			break;
+		}
+		write_unlock(&resource_lock);
+
+		list_add(&good->list, &head);
+	}
+
+	/* pick up the smallest one */
 	write_lock(&resource_lock);
-	err = find_resource(root, new, size, &constraint);
+	list_for_each_entry(good, &head, list) {
+		if (resource_size(&good->avail) < avail_size) {
+			avail_size = resource_size(&good->avail);
+			new->start = good->new.start;
+			new->end = good->new.end;
+			err = 0;
+		}
+		__release_resource(&good->avail);
+	}
 	if (err >= 0 && __request_resource(root, new))
 		err = -EBUSY;
 	write_unlock(&resource_lock);
+
+	/* delete the list */
+	list_for_each_entry_safe(good, tmp, &head, list) {
+		list_del(&good->list);
+		kfree(good);
+	}
+
 	return err;
 }
 
-- 
1.8.4.5